As disclosed in U.S. Pat. Nos. 4,482,669 (Seyferth et al.-I), 4,645,807 (Seyferth et al.-II), 4,650,837 (Seyferth et al.-III), and 4,659,850 (Arai et al.), it is known that polysilazanes are useful as preceramic materials; and Seyferth et al.-I teach that their polysilazanes are especially useful as binders for ceramic powders, such as silicon carbide and silicon nitride.
Copending applications Ser. No. 120,102 (Semen et al.-I), filed Nov. 13, 1987; Ser. No. 193,105 (Semen et al.-II), filed May 12, 1988; and Ser. No. 233,369 (Semen et al.-III), filed Aug. 18, 1988, teach that low density polysilazane-derived ceramics having improved strength can be obtained by employing as preceramic molding compositions certain intimate mixtures of silicon carbide or silicon nitride with polysilazanes in which the particle size of the mixtures has been reduced to not larger than about 105 micrometers.
The preceramic compositions of Semen et al.-I, II, and III provide ceramics which are useful in many applications. However, in other applications, such as pump parts, they do not have as much wear resistance as might be desired.
Lewis, Materials Engineering. Vol. 106, No. 5, pp. 39-41, May, 1989, states that the presence of a high level of residual graphite in silicon carbide gives excellent wear resistance in such applications as sand slurry pump seals, water pumps, and bearings and seals for corrosive and abrasive service.